Zircon U/Pb dating and Hf-O isotopes of the Zhouan ultramafic intrusion in the northern margin of the Yangtze Block,SW China:Constraints on the nature of mantle source and timing of the supercontinent Rodinia breakup  

作　　者：WANG MengXi WANG ChristinaYan ZHAO JunHong 

机构地区：[1]Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences [2]Graduate University of Chinese Academy of Sciences [3]Department of Earth Sciences,China University of Geosciences

出　　处：《Science China(Technological Sciences)》2013年第3期777-787,共11页中国科学（技术科学英文版）

基　　金：supported by the National Natural Science Foundation of China(40972060and41073026);the Hundred Talents Program of the Chinese Academy of Sciences

摘　　要：The Zhouan ultramafic intrusion in the northern margin of the Yangtze Block is mainly composed of lherzolite. Zircon grains selected from lherzolite are irregular in shape with distinct oscillatory and sector zoning and have Th/U ratios ranging from 0.8 to 10.6, indicating a magmafic origin. The weighted average 206pb/238U age is 637±4 Ma （2σ, n=15）, which can be considered as the crystallization age of the Zhouan intrusion. Zircon grains have δ18O values ranging from 5.2‰to 7.0‰, with an averaged value of 5.8±0.4‰（1 or, n=33）, similar to the mantle δ18O value of zircon. Their 176Hf/177Hf（t） ratios range from 0.282410 to 0.282594 with εHf（t） values ranging from 1.3 to 7.6, lower than the corresponding value of the depleted mantle （~15）, indicating an enriched mantle source. The enriched mantle source may have generated from a metasomatized lithospheric mantle with subducted slab. A number of -635 Ma mafic-ultramafic intrusions in the Suizao basin are associated with coeval bimodal volcanics of the Yaolinghe Formation, indicating a continental rift setting. The ~635 Ma magmafic event in this region may represent the product of the last breakup of the Rodinia supercontinent in the northern margin of the Yangtze Block at Neoproterozoic.

关 键 词：zircon Hf-O isotopes Zhouan ultramafic intrusion northern margin of the Yangtze Block Neoproterozoic 

分 类 号：P542[天文地球—构造地质学] P588.1[天文地球—地质学]